Effect of body mass index (BMI) on estimation of extracellular volume (ECV) in hemodialysis (HD) patients using segmental and whole body bioimpedance analysis

The aim of the study was to investigate whether body mass index (BMI) influences the estimation of extracellular volume (ECV) in hemodialysis (HD) patients when using segmental bioimpedance analysis (SBIA) compared to wrist-to-ankle bioimpedance analysis (WBIA) during HD with ultrafiltration (UF). Twenty five HD patients (M:F 19:6,) were studied, and further subdivided into two groups of patients, one group with a high BMI (⩾25 kg m⁻²) and the other with a low BMI (<25 kg m⁻²). Segmental (arm, trunk, leg) and wrist-to-ankle bioimpedance measurements on each patient were performed using a modified Xitron 4000B system (Xitron Technologies, San Diego, CA). No differences in extracellular resistance (R_E, ohms) between wrist-to-ankle (R_W) and sum of segments (R_S) were noted for either the high BMI (489.2 ± 82 ohm versus 491.6 ± 82 ohm, p = ns) or low BMI groups (560.8 ± 77 ohm versus 557.5 ± 75 ohm, p = ns). UF volume (UFV, liters) did not differ significantly between the groups (4.0 ± 0.9 L versus 3.3 ± 1.0 L, p = ns), but change in ECV (ΔECV) differed not only between methods: WBIA versus SBIA in the high BMI group (2.74 ± 1.1 L versus 3.64 ± 1.4 L, p < 0.001) and in the low BMI group (1.86 ± 0.9 L versus 2.91 ± 1.0 L, p < 0.05) but also between the high and lower BMI groups with WBIA (2.74 ± 1.1 L versus 1.86 ± 0.9 L, p < 0.01). However, there was no significant difference in SBIA between BMI groups. This study suggests that the segmental bioimpedance approach may more accurately reflect changes in ECV during HD with UF than whole body impedance measurements.